French patent publication No. 2,276,798 discloses a seat having a pair of side support panels whose position is adjustable using a pair of U-shaped tubular frame members. The base of the U-shaped frame extends forward, and the posterior ends have a pair of holes. These holes are slipped onto bearing pins integral with the seat back frame such that the U-shaped frame members may pivot. Each U-shaped frame member is urged outwardly by a separate flexural spring. The angle through which the frame members can pivot is limited by a stop portion which contacts a portion of the frame.
This known device is costly, insofar as it requires the use of relatively costly bearing pins, requires that the pins be in accurate alignment with one another, and requires mounting a separate spring element as part of the assembly.